It is known in the prior art to recover elemental sulfur from hydrogen sulfide-containing gas streams as is set forth in the article "Fundamentals of Sulfur Recovered by the Claus Process" by B. Gene Goar, published in the 1977 Gas Conditioning Conference Report.
It is also known to use oxygen-enrichment in the operation of a Claus sulfur plant to increase the capacity of hydrogen sulfide treated in a plant as set forth in the article "Oxygen Use in Claus Sulfur Plants" by M. R. Gray and W. Y. Svrcek, published in the 1981 Gas Conditioning Conference Report. In that article it was disclosed that oxygen can be added to the air feed to the burner of the reaction furnace in a Claus sulfur plant to increase the amount of hydrogen sulfide which is combusted to sulfur dioxide for later catalytic conversion to elemental liquid sulfur product. The article recites that the maximum capacity increase which can be achieved with oxygen enrichment is determined by the pressure drop through the plant, the reactor space velocity and temperatures of the reaction furnace and the various catalytic zones, particularly the refractory materials used in the furnace superstructures of the Claus plant.
In the 1983 publication by Linde of Union Carbide entitled "Claus Plant Oxygen Enrichment", it is noted that oxygen-enrichment limitations exist for rich hydrogen sulfide streams due to temperature limits in the furnace or waste heat boiler of the Claus plant.
U.S. Pat. No. 3,822,341 discloses a Claus plant which uses oxygen-enrichment. One source of the oxygen is initially used to strip residual SO.sub.2 from a sidestream in vessel 92, before the oxygen stream in line 96 is optionally recycled to be included with the oxygen in line 12 going to the combustion zone of the waste heat boiler 8, as recited at column 5, lines 65-68 of the specification. Because the oxygen content of such a stream is completely consumed in an exothermic reaction, this stream cannot be utilized as a moderating medium for flame temperature of the reaction furnace. As described by the Goar article above, Claus sulfur plants typically have an adiabatic reaction furnace followed by waste heat boiler. The excessive temperature problem with oxygen enriched operation occurs in the adiabatic reaction furnace. U.S. Pat. No. 3,822,341 ignores the existence of this problem.
U.S. Pat. No. 4,153,674 discloses a Claus plant and tailgas clean up plant wherein a gas stream in line 20 is removed from a tailgas system and is returned or recycled to the front end of the Claus plant 7. This patent does not consider oxygen-enrichment or flame temperature moderation by a recycle stream. Also, the tailgas is reacted to convert all sulfur to hydrogen sulfide, which is adsorbed, stripped and returned to the Claus plant.
U.S. Pat. No. 4,279,882 discloses a sulfur recovery process, which uses only a series of catalytic reaction beds rather than a combustion reaction furnace, as in the traditional Claus plant. A temperature modifying recycle stream is set forth in the patent, wherein stream 26 is returned to the feed in order to control the temperature in the catalytic reaction zones. This process is economical only for dilute hydrogen sulfide feed gas applications. It also requires a recycle blower operating at high temperature.
The present invention overcomes the shortcomings of the prior art by increasing throughput of a Claus plant with an oxygen-enrichment to an extent beyond that contemplated in the prior art due to flame temperature limitations. This is achieved by injecting water into the reaction furnace of the Claus plant in order to moderate the flame temperatures. This water injection moderates any increases in pressure drop, which would be caused by recycling inerts from a particular downstream portion of the process. It also avoids the need for a recycle blower.